Thomson box records from Welsh transmitter?

Even though I set recordings for BBC1, 2 etc, invariably, the recordings are made from BBC1 Wales, BBC2 Wales etc. The problem is that the quality of recording is poor, either blank or stuttering. This has only happned for thr past 6 months or so-our digital switchover took place about 3 years ago. I know that the transmitter in North Wales covers our area but it is not supposed to be the main transmitter. Any ideas?